The present invention relates to a semiconductor light emitting device having a double-hetero structure in which a first conductive type layer, an active layer, and a second conductive type layer are stacked, an image display unit and a lighting apparatus using the semiconductor light emitting device and a method of fabricating the semiconductor light emitting device. In particular, the present invention relates to a semiconductor light emitting device capable of enhancing the light emergence efficiency and a method of fabricating the semiconductor light emitting device.
Various methods have been proposed to enhance luminous of a semiconductor light emitting device. Such methods are mainly classified into a technique of increasing a quantity of light emission generated in a device to an input current of the device, and a technique of increasing a light emergence efficiency; that is, a characteristic to allow light generated in a device to efficiently emerge outwardly from the device. The former technique is greatly dependent on materials forming crystal layers, a crystal structure, a crystal growth characteristic, a combination of the crystal layers, and a fabrication process. The latter technique is intended to allow light generated in a device to emerge outwardly from the device without attenuation of the light; that is, without leakage of the light in consideration of a device structure and reflectance of light due to the device structure at the time when the device is mounted to an apparatus board.
In particular, the latter technique has a difficulty in that if light generated in a light emission region of a semiconductor light emitting device enters a light emergence plane at a large incident angle, such light is not allowed to emerge outwardly from the device due to total reflection. To cope with such an inconvenience, there has been proposed a method of allowing light totally reflected from a boundary plane of a device housed in a package to be reflected again from an inner mirror provided in the package and hence to emerge outwardly from the device, and a method of allowing light generated in a semiconductor light emitting device to be directly reflected from an inner mirror with its angle adjusted provided in a package and hence to emerge outwardly from the device. Also, there is known a method of suppressing a reduction in light emergence efficiency due to total reflection for a semiconductor light emitting device having a structure called a “planar type structure” in which crystal layers are grown on a plane parallel to a crystal growth substrate. According to this method, light generated from the crystal layer forming a light emission region in random directions is adjusted in one direction by an external mirror housed in a package.
Other methods of increasing a light emergence efficiency have been proposed. For example, a light emitting device having a semiconductor light emitting device main body including a light emission region and a device mounting portion including a light reflecting portion, which is provided separately from the device, has been known from Japanese Patent Laid-open No. Hei 9-51124.
On the other hand, in recent years, semiconductor light emitting devices for adjusting an angle of light, not by a reflecting mirror or the like housed in a package, but by an electrode provided in the device have been proposed. For example, a semiconductor light emitting device having a pyramid shape using a gallium nitride based compound semiconductor as a material for a crystal layer has been known. In this device, a quantity of light emission generated in the device to an input current of the device can be increased and the light emergence efficiency can be increased irrespective of the package structure.
By the way, for a semiconductor light emitting device by growing crystal on a flat principal plane of a substrate having a specific crystal plane by epitaxial growth, a boundary plane between the substrate and the crystal layer is flatted. In this case, if the back plane of a crystal layer, at which the substrate is joined to the device, is taken as a light emergence plane, part of light generated in the device is not allowed to emerge outwardly from the device due to total reflection, thereby failing to increase the light emergence efficiency.
In the case of fabricating a planar image display unit requiring a light control board for adjusting the optical path in one direction or the like, in addition to each device main body including a light emission region, it is difficult to display an image with a high resolution by arraying fine devices and controlling light emission for each of the devices.
Accordingly, it has been required to develop a high performance image display unit and a high performance lighting apparatus, each of which is capable of reducing the quantity of part of the light generated from a light emission region in random directions, which part is not allowed to emerge outwardly from the device due to total reflection from a light emergence plane, to increase the light emergence efficiency, thereby preparing devices with high luminescence without changing the sizes of the devices, and miniaturizing the sizes of the devices and arraying the miniaturized devices.
In particular, for a pyramid-shaped semiconductor light emitting device, the light emergence efficiency has been improved by allowing light generated from a light emission region of the device in random directions to be subjected to multi-reflection from an electrode formed on a tilt plane. However, the tilt plane on which the electrode is formed is set to a specific angle to a light emergence plane, so that there remains part of the light entering the light emergence plane at an angle allowing total reflection. As a result, it fails to further increase the light emergence efficiency and to sufficiently achieve the performance of the device.